The invention pertains to a chromium-containing cemented carbide body (e.g., a coated cemented (cobalt-chromium binder alloy) tungsten carbide cutting insert) that has a surface zone of binder alloy enrichment.
Coated cemented carbide (e.g., cemented [cobalt] tungsten carbide) cutting inserts that exhibit a surface zone of binder enrichment are in use for metal cutting applications. The surface zone of binder enrichment may be stratified such as shown in the article xe2x80x9cThe Microstructural Features and Cutting Performance of the High Edge Strength Kennametal Grade KC850xe2x80x9d, Proceedings of the Tenth Plansee Seminar, Reutte, Trol, Austria, Metalwerke Plansee A. G. (1981), pp. 613-627. The surface zone of binder enrichment may be non-stratified such as shown in U.S. Reissue Pat. No. 34,180 to Nemeth et al. or U.S. Pat. No. 5,955,186 to Grab.
Current coated cemented carbide cutting inserts that exhibit a surface zone of binder enrichment have acceptable performance characteristics. However, it would still be desirable to provide a coated cemented carbide cutting insert that has improved performance characteristics.
In one form thereof, the invention is a cutting insert having a tungsten carbide based bulk composition of at least 70 weight percent tungsten and carbon, between about 3 weight percent and about 12 weight percent cobalt, and at least 0.09 weight percent chromium. The cobalt and chromium form a binder alloy. The binder alloy content of the composition is enriched in a surface zone beginning near and extending inwardly from the peripheral surface of the substrate.
The substrate also preferably contains nitrogen as a result of the mechanism used to obtain binder enrichment.
Preferably, the tungsten carbide based bulk composition has up to about 10 weight percent tantalum, up to about 6 weight percent niobium, and up to about 10 weight percent titanium.
Preferably, there is at least one weight percent total of tantalum, niobium, and titanium, and more preferably, at least two weight percent total of tantalum, niobium, and titanium.
Preferably, the ratio of the weight percent of chromium to the weight percent of cobalt ranges between about 0.03 to about 0.15, and more preferably, between about 0.05 to 0.10.
Preferably, the ratio of the weight percent of chromium to the weight percent cobalt remains about constant between the surface zone of binder alloy enrichment and the bulk composition.
Preferably, the cutting insert in accordance with the invention has a substrate composition as described above and a hard coating thereon composed of one or more layers. Preferably, the innermost layer contains chromium, which has diffused into the layer from the substrate during chemical vapor deposition of the coating onto the substrate, preferably forming a chromium containing solid solution layer (e.g., a titanium chromium carbonitride, or a titanium tungsten chromium carbonitride).
These and other aspects of the invention will become more clear upon review of the following detailed description of the invention in conjunction with the drawings.